Method of thermally treating silicon with oxygen

ABSTRACT

A method and apparatus for oxidizing materials used in semiconductor integrated circuits, for example, for oxidizing silicon to form a dielectric gate. An ozonator is capable of producing a stream of least 70% ozone. The ozone passes into an RTP chamber through a water-cooled injector projecting into the chamber. Other gases such as hydrogen to increase oxidation rate, diluent gas such as nitrogen or O 2 , enter the chamber through another inlet. The chamber is maintained at a low pressure below 20 Torr and the substrate is advantageously maintained at a temperature less than 800° C. Alternatively, the oxidation may be performed in an LPCVD chamber including a pedestal heater and a showerhead gas injector in opposition to the pedestal.

RELATED APPLICATION

This application is a division of Ser. No. 11/099,082, filed Apr. 5,2005, and to be issued as U.S. Pat. No. 7,972,441 on Jul. 5, 2011. Thisapplication is also related to Ser. No. 11/530,375, filed Sep. 8, 2006and now abandoned.

FIELD OF THE INVENTION

The invention relates generally to fabrication of integrated circuits.In particular, the invention relates to thermal oxidation of and otheroxygen-based treatment of electronic materials such as silicon.

BACKGROUND ART

The fabrication of silicon integrated circuits typically includes one ormore steps of forming layers of silicon dioxide, having a generalcomposition of SiO₂, although some variation in its stoichiometry ispossible. In some applications, dopants are added. For brevity, thismaterial may hereafter be referred to as oxide. Silicon dioxide is arugged material that bonds well with silicon and is electricallyinsulating, that is, dielectric. Thicker layers of oxide are typicallydeposited by spin-on glasses or by chemical vapor deposition,particularly when they form inter-level dielectric layers, which may beformed over metal and other oxide features. However, thin oxide layersformed over silicon may be formed by oxidizing the silicon to formsilicon oxide. The silicon to be oxidized may be monocrystalline siliconof the wafer or polysilicon deposited as a layer on the wafer in amulti-level structure. Gate oxide layers may be formed by oxidation oftypically about 1 nm or less. Pads and STI (shallow trench isolation)liners may similarly be formed to thicknesses of typically 5 to 10 nm.The oxide layer not only electrically insulates the underlying siliconbut also passivates the silicon/dielectric interface.

Oxidation is conventionally performed by heating the silicon surface toapproximately 1000° C. to 1200° C. or higher and exposing it to gaseousoxygen for dry oxidation or to steam (H₂O) for wet oxidation. Suchthermal oxidation may conventionally be performed in a furnaceaccommodating large number of wafers, but furnaces have in part beensuperseded by single-wafer processing chambers utilizing a processcalled rapid thermal oxidation (RTO), a form of rapid thermal processing(RTP). In RTO, high-intensity incandescent lamps rapidly heat a siliconwafer to very high temperatures and oxygen is flowed into the RTPchamber to react on the surface of the hot wafer to react with thesilicon and produce a layer of silicon oxide on top of the wafer. Gronetet al. disclose oxidation in an RTP chamber in U.S. Pat. No. 6,037,273,incorporated herein by reference in its entirety. One advantage of RTOis that the walls of the RTP chamber are typically much cooler than thewafer so that oxidation of the chamber walls is reduced. Gronet et al.disclose injecting oxygen and hydrogen gases into the RTP chamber toreact near the hot wafer surface for in situ generation of steam.

It has been recognized that oxygen radicals O* provide severaladvantages in silicon oxidation. The oxygen radicals more easily reactthan oxygen gas so that the oxidation rate is increased for a giventemperature. Further, the radicals promote corner rounding, an importantfeature in STI.

Oxygen plasmas have been used for oxidation, but they are felt tosubject the semiconducting silicon and dielectric layers to damageparticularly when the oxygen species is charged, e.g. O⁻ or O⁼.

Ozone (O₃) is an unstable form of oxygen gas that may be considered anoxygen radical since O₃ spontaneously dissociates into O₂ and O*,particularly when exposed to surfaces held at temperatures of greaterthan 400° C. It is known to use ozone in silicon oxidation, see U.S.Pat. No. 5,294,571 to Fujishiro et al. and U.S. Pat. No. 5,693,578 toNakanishi et al. However, most known prior art for ozone-assistedoxidation occurs at relatively high temperatures and low ozoneconcentrations.

Another approach for low temperature oxidation supplies the reactorchamber with a gas mixture of oxygen gas O₂ and ozone O₃, as disclosedin U.S. Pat. No. 5,330,935 to Dobuzinsky et al. (hereafter Dobuzinsky).Ozone is a metastable form of oxygen that may be generated in amicrowave or UV generator and which readily dissociates into O₂ and theoxygen radical O*. Dobuzinsky supplies the ozone-rich mixture into athermal reactor operated at a relatively low temperature but includingadditional RF plasma excitation of the ozone. However, Dobuzinsky'sreactor is still a hot-wall reactor so that the ozone quicklydissociates inside the chamber and equally reacts with the chamberwalls. Dobuzinsky does however mention the possibility of RTO aftertheir plasma oxidation.

More recent technology has imposed different constraints upon siliconoxidation processes. In view of the very thin layers and shallow dopingprofiles in advanced integrated circuits, the overall thermal budget andmaximum processing temperatures are reduced. That is, the typicaloxidation temperatures of greater than 1000° C. are considered excessiveeven when used with the rapid temperature ramp rates available in RTP.Furthermore, the gate oxide thickness are decreasing to well below 1 nm,for example, 0.3 to 0.6 nm in the near future. However, to preventdielectric breakdown and increase reliability, the gate oxides must beuniformly thick and of high quality. Plasma oxidation may be a lowtemperature process because it produces oxygen radicals O* which readilyreact with silicon at low temperatures. However, charging and othereffects on the fragile thin oxide prevent plasma oxidation from beingwidely adopted. The fabrication of advanced integrated circuits is notonly constrained by a reduced thermal budget, they it is also facingdecreasing limits in the maximum temperature to which the ICs may beexposed even for short times. The known prior art of ozone oxidationdoes not satisfy the more recent requirements.

It is felt that the prior art insufficiently utilizes the advantages ofozone for low temperature oxidation without the use of plasmas.

Furthermore, ozone is considered explosive. Safety concerns are greatlyalleviated if the pressure within a chamber containing ozone is held ata pressure of no more than 20 Torr. Such low pressures, however,disadvantageously decrease the oxidation rate.

SUMMARY OF THE INVENTION

Silicon or other material in a semiconductor substrate is oxidized byexposing it to a high concentration of ozone at a relatively lowtemperature, for example, between 400 and 800° C. in a plasma-freeprocess. Even lower temperatures are possible. The processing chambermay be maintained at a relatively low pressure, for example, less than20 Torr, which low pressure simplifies the safety requirements. Thepressure may be even lower, for example, less than 10 Torr or even lessthan 5 Torr. The invention is particularly useful for growing a gateoxide or a passivation layer on silicon.

The ozone may be produced in an ozonator, which includes several typesof apparatus producing ozone from oxygen. The ozonator should be capableof producing a stream of oxygen-containing gas that is at least 30%ozone, more preferably 70% ozone, still more preferably at least 80%,and even more preferably at least 90%.

The ozone may be combined with a diluent gas such as oxygen gas ornitrogen.

The ozone/oxygen mixture may be combined with hydrogen to increase theoxidation rate. The hydrogen may be essentially pure hydrogen gas or bea forming gas of H₂/N₂, for example, having 7% hydrogen.

The ozone/oxygen mixture may be combined with a nitriding gas such asnitrous oxide or ammonia so that the oxidation product is a siliconoxynitride.

The oxidation may be performed in a rapid thermal processing (RTP)chamber including an array of incandescent lamps or a scanned lasersource to radiantly heat the substrate.

The ozone is preferably introduced into the RTP processing chamber in afirst inlet port separate and offset from a second inlet port supplyingthe diluent gas of oxygen or nitrogen, hydrogen, and nitriding gas.Preferably, the two ports are angularly spaced on the chamber wall witha separation of between 15° and 120°, 90° being a preferred separation.The first inlet port for the ozone preferably includes a cooled injectorthat projects into the processing chamber and is cooled by water orother cooling fluid.

Alternatively, the oxidation may be performed in a low-pressure chemicalvapor deposition (LPCVD) chamber including an electrically heatedpedestal supporting and heating the substrate and a showerheadpositioned in opposition to the substrate. The showerhead includes asupply manifold in which the ozone/oxygen gas and other gases may bemixed and a large number of apertures between the manifold and theprocessing chamber over an area approximately covering the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating a rapidthermal processing (RTP) chamber capable of performing ozone-basedthermal oxidation.

FIG. 2 is an exploded orthographic view of a water-cooled gas injector.

FIG. 3 is a sectioned orthographic view of the injector of FIG. 2.

FIG. 4 is a cross-sectional view of the injector of FIG. 2.

FIG. 5 is an axial plan view of the injector of FIG. 2.

FIG. 6 is a schematic cross-sectional view of the RTP chamber takenalong its central axis.

FIG. 7 is a cross-sectional view schematically illustrating alow-pressure chemical vapor deposition (LPCVD) chamber configured forozone-based thermal oxidation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention in part concerns the thermal oxidation of silicon or othermaterials in the presence of ozone in an RTP (rapid thermal processing)chamber or in a chamber adapted for chemical vapor deposition.

FIG. 1 schematically illustrates in cross section an RTP chamber 10described by Ranish et al. in U.S. Pat. No. 6,376,804, incorporatedherein by reference. The chamber 12 is generally representative of theRadiance RTP chamber available from Applied Materials, Inc. of SantaClara, Calif. The RTP chamber 10 includes a vacuum chamber 12, a wafersupport 14 located within the chamber 12, and a lamphead 16 or heatsource assembly located on the top of the chamber 12, all generallysymmetrically arranged about a central axis 18.

The vacuum chamber 12 includes a chamber body 20 and a window 22 restingon the chamber body 20. The window 22 is composed of a material that istransparent to infrared light, for example, clear fused silica quartz.

The chamber body 20 may be made of stainless steel and be lined with aquartz liner (not shown). An annular channel 24 is formed symmetricallyabout the central axis 18 near the bottom of the chamber body 20. Thewafer support 14 includes a magnetic rotor 26 placed within the channel24, a quartz tubular riser 28 resting on or otherwise coupled to themagnetic rotor 26, and an edge ring 30 resting on the riser 28. The edgering 30 may be composed of silicon, silicon-coated silicon carbide,opaque silicon carbide, or graphite. During processing, a wafer 34 orother substrate rests on the edge ring 30 in opposition to the window22. A purge ring 36 outside and below the edge ring 30 supplies a purgegas such as argon to the back of the wafer 34. A magnetic stator 40located externally of the magnetic rotor 26 is magnetically coupledthrough the chamber body 20 to the magnetic rotor 26. The rotor 26 maybe mechanically supported on ball bearings or be magnetically levitatedby the magnetic rotor 26. When an unillustrated motor rotates themagnetic stator 34 about the central axis 18, it induces rotation of themagnetic rotor 26 and hence of the edge ring 30 and the supported wafer34 about the central axis 18.

The quartz window 22 rests on an upper edge of the chamber body 20 andan O-ring 44 located between the window 22 and the chamber body 20provides a vacuum seal between them. A lamphead body 46 of the lamphead16 rests on the window 20. Another O-ring 48 located between the window20 and lamphead body 46 provides a vacuum seal between them when a clamp49 presses together the chamber body 20 and the lamphead body 46 withthe window 22 and O-rings 40, 48 sandwiched between them. Avacuum-sealed processing space 50 is thereby formed within the chamberbody 20 below the window 22 and encompasses the wafer 34 to beprocessed. The wafer 34 is transferred into and out of the processingchamber by means of an unillustrated wafer port in the sidewall of thechamber body 20, a slit valve selectively sealing the wafer port, awafer paddle insertable through the wafer port, and lift pins in abottom wall 52 of the chamber body 20 which selectively raise the wafer34 above the edge ring 30 and the paddle. The top surface of the bottomwall 52 may be coated with a reflective layer to act as a reflectorplate defining one side of a black body cavity 54 on the backside of thewafer 34.

The lamphead 16 includes a plurality of lamps 56 loosely disposed inrespective downwardly directly lamp holes 58. The lamps 56 are supportedby and electrically powered through electrical sockets 60. The lamps 56are preferably incandescent bulbs that emit strongly in the infraredsuch as tungsten halogen bulb having a tungsten filament inside a quartzbulb 62 filled with a gas containing a halogen gas such as bromine anddiluted with an inert gas to clean the inside of the quartz bulb 62. Theupper portion of each bulb 62 and its socket 60 are potted into its lamphole 58 with a ceramic potting compound 64, which is relatively porous.The lamps 56 are located inside the reflective walls of the verticallyoriented cylindrical lamp holes 58 within the lamphead body 46 to formrespective light pipes. The open ends of the lamp holes 58 of thelamphead body 46 are located adjacent to but separated from the window20.

Interconnected cooling channels 66 are defined within the lamphead body40 by upper and lower lamphead chamber walls 68, 70 and cylindricalwalls 72 surrounding each of the lamp holes 58 as well as an exteriorside wall 74 of the lamphead body 46. A recirculating coolant, such aswater, introduced into the chambers 66 via an inlet 76 and removed at anoutlet 78 cools the lamphead body 46 and traveling adjacent the lampholes 58 cools the lamps 56. Baffles may be included to ensure properflow of the coolant through the cooling channels 66.

A thermally conductive gas, such as helium, is supplied from apressurized gas source 84 and metered by a mass flow controller 86 to bedelivered to the lamphead 16 to facilitate thermal transfer between thelamps 56 and the cooling channels 66. The helium is supplied through aport 88 to a manifold 90 formed in back of the lamp bases between thelamp holes 58 and a lamphead cover 92. Opening the mass flow controller86 causes the thermal transfer gas to flow into the manifold 90 andfurther flow through the porous potting compound 64 around the sides ofthe bulb 62 of each lamp 56 to cool by heat convectively transferredthrough the thermal transfer gas to the cooling water in the channels66.

A vacuum pump 100 reduces the pressure within the lamphead body 46,particularly when the processing chamber 50 within the chamber 12 isvacuum pumped so that the reduced pressure in the lamphead body 46reduces the pressure differential across the quartz window 20. Thevacuum pump 100 is connected to the air passages in the lamp holes 58surrounding the lamps 56 through a port 102 including a valve 104. Thepumping of the vacuum pump 100 must be balanced with the supply ofhelium from the gas source 84 to maintain the desired pressure of heliumwithin the lamphead 16 for promoting thermal transfer.

Thermal sensors such as seven pyrometers 110 (only two of which areshown) are supported by the chamber body 20 and are optically coupled tolight pipes 112 disposed in respective apertures 114 in the bottom wall52. The pyrometers 110 detect respective temperatures or other thermalproperties at different radial portion of the lower surface of the wafer34 or of the edge ring 30, as described in U.S. Pat. No. 5,755,511 toPeuse et al. The pyrometers 110 supply temperature signals to a powersupply controller 116, which controls the power supplied to the infraredlamps 56 in response to the measured temperatures. The infrared lamps 56may be controlled in radially arranged zones, for example, fifteenzones, to provide a more tailored radial thermal profile to compensatefor thermal edge effects. All the pyrometers 110 together providesignals indicative of a temperature profile across the wafer 34 to thepower supply controller 116, which controls the power supplied to eachof the zones of the infrared lamps 56 in response to the measuredtemperature profile.

The chamber body 20 of the processing chamber 12 includes twoperpendicularly arranged processing gas inlet ports 120, 122 (inlet port122 is not illustrated in FIG. 1). In use, the pressure within theprocess space 50 can be reduced to a sub-atmospheric pressure prior tointroducing a process gas through the gas inlet ports 120, 122. Theprocess space 50 is evacuated by a vacuum pump 124 pumping through apump port 126 arranged diametrically opposite the first inlet port 120.The pumping is largely controlled by a butterfly valve 128 disposedbetween the pump port 126 and the vacuum pump 124. The pressure may bereduced to between about 1 and 160 Torr. However, for reasons to bedescribed below, the chamber pressure is preferably maintained at lessthan 20 Torr.

Although the RTP chamber 10 represents the most prevalent type of RTPchamber in use today, advanced RTP chambers are being developed usingone or more lasers whose beams are scanned over the substrate, as hasbeen disclosed by Jennings et al. in U.S. Patent Application PublicationUS 2003/0196996 A1, incorporated herein by reference in its entirety.

According to one aspect of the invention involving oxidation, a gassource 130 supplies oxygen gas (O₂) through a mass flow controller 122to an ozonator 134, which converts a large fraction of the oxygen toozone gas (O₃). The resultant oxygen-based mixture of O₂ and O₃ andperhaps some oxygen radicals O* and ionized oxygen atoms or molecules isdelivered through a process gas supply line 136 to the first inlet port120 and into the processing chamber 50, The oxygen-based gas reactswithin the processing chamber 50 with the surface of the wafer 34, whichhas been heated to a predetermined, preferably low temperature by theinfrared lamps 56. Ozone is a metastable molecule which spontaneouslyquickly dissociates in the reactionO₃→O₂+O*,where O* is a radical, which very quickly reacts with whatever availablematerial can be oxidized. In general, ozone dissociates on any surfacehaving a temperature greater than 400° C. although it also dissociatesat a lower rate at lower temperatures.

The ozonator 134 may be implemented in a number of forms including acapacitively or inductively coupled plasma or a UV lamp source. It ispreferred that the ozonator be capable of a stream of gas containing atleast 70% ozone, more preferably at least 80%, and most preferably atleast 90%. Even an ozone concentration of at least 30% would provideadvantages over the prior art. An ozonator capable of producing thehigher ozone concentrations is commercially available from IwatamiInternational Corp. of Osaka, Japan as Model AP-800-LR. Other ozonatorsand sources of ozone may be used with the invention.

At these high ozone concentrations, the wafer need not be heated verymuch to achieve relatively high oxidation rates. The high ozoneconcentration also allows the ozone partial pressure to be reduced.Safety rules in place in many countries require that special proceduresand equipment be implemented whenever ozone is present at pressures ofgreater than 20 Torr. Below 20 Torr, the strict rules do not apply.Accordingly, a high ozone fraction allows the ozone oxidation to beperformed at pressures of less than 20 Torr.

Highly concentrated ozone may be used not only to oxidize bare siliconbut may be used in a two-step process. In the first step, a thin oxideis grown perhaps using only oxygen at a relatively low temperature. Inthe second step, concentrated ozone is used to treat the preexistingoxide film and to increase its thickness to a reliable level. Theconcentrated ozone may also be used to treat and possibly increase thethickness of a metal oxide film, such as tantalum oxynitride (TaNO).Similarly, high-k dielectric films, for example, of perovskite material,may be treated with concentrated ozone to stabilize them and for otherreasons.

One problem with ozone oxidation is that a high temperature, forexample, above 400° C., of any surface to which the ozone is exposedpromotes the dissociation of ozone before it reaches the hot wafersurface. As a result, the ozone should be maintained relatively coolexcept adjacent the wafer being oxidized. An RTP chamber is advantageousfor ozone oxidation because it may be considered to be a cold-wallreactor in which the chamber walls are typically much cooler than theradiantly heated wafer. In contrast, in a hot-wall reactor such as anannealing furnace, the wafer temperature is no more than the temperatureof the surrounding furnace wall or liner. Although high wafertemperatures are achievable in RTP chambers, a sidewall 138 of theprocessing chamber 50 and the window 22 are typically maintained at muchlower temperatures, particularly if the thermal process performed over arelatively short period. Nonetheless, even the walls of an RTP chamberbecome somewhat warm and any ozone adjacent the warm walls is likely todissociate far from the wafer and perhaps oxidize the chamber wallrather than the wafer.

To reduce the effect of a warm chamber, the ozone is supplied into thechamber through an injector 140 which projects from the chamber sidewall138 towards the center 18 of the processing chamber 50 parallel andabove the surface of the wafer 34. In one embodiment, the nozzle tip ofthe injector 140 is radially spaced about 2.5 cm outwardly of the edgeof the wafer 34. Furthermore, the injector 140 is preferably watercooled or otherwise temperature controlled by a fluid.

One embodiment of the injector 140 is illustrated in the orthographicview of FIG. 2, the sectioned orthographic view of FIG. 3, and thecross-sectional view of FIG. 4. A base 142 can be screwed to theexterior of the chamber sidewall 138 and sealed to it in a configurationhaving an tubular body 144 of a length of about 5 cm projecting into theprocessing chamber 50. A washer 146 is welded to the end of the tubularbody 144 to seal the end of the tubular body 144 except for an injectornozzle 148 penetrating through and welded to the hole of the washer 146.A plan view of the tubular body 144 shown in FIG. 5 is taken along line5-5 of FIG. 4 along the axis of the tubular body 144. For clarity, theviews of FIGS. 3, 4, and 5 omit the washer 146.

A central gas line 150 is machined in the tubular body 144 andterminates at the injector nozzle 148 at its distal end. A supply tube152 is fixed to the base 142 and communicates with the central gas line150. A gland 154 captures the end of the supply tube 152 and is threadedonto the gas supply line 136 from the ozonator 134 of FIG. 1. Twocircular axially extending liquid lines 158, 160 are bored into thetubular body 144 offset from the tube's central axis but stop beforereaching the bottom of the base 142. Instead, two obliquely orientedfluid lines 162, 164 are bored from the outside of the base 142 to meetwith the axial liquid lines 158, 160 on their inner ends and to be matedwith corresponding tubes and glands on their outer ends and thereby becoupled by two recirculating chilling lines 166, 168, illustrated inFIG. 1, to the two ports of a chiller 170. The chiller 170 eithersupplies cold water or recirculates cooling water or other coolingliquid or fluid refrigerant through the injector 140 to cool it and theinjected ozone.

Returning to FIGS. 2-5, two axially extending, arc-shaped apertures 180,182 are machined in the distal portion of the tubular body 144 to berespectively connected to the two axial liquid lines 158, 160. A septum184 separates the two arc-shaped apertures 180, 182, and the distal endof the gas line 150 is formed within the septum 184. An annular ledge186 is machined into the distal end of the tubular body 144 at a levelslightly above the end surface of the septum 184. The washer 146 restson the ledge 186 and is welded to the outer portion of the tubular body144 and to the injector nozzle 148. Thereby, cooling water supplied byone liquid line 158 flows through one arc-shaped aperture 180surrounding almost half of the distal portion of the gas supply line160, flows through the gap between the end surface of the septum 184 andthe washer 146 and into the other arc-shaped aperture 182 surroundingmost of the other half of the distal portion of the tubular body 144before flowing out through the other liquid line 160.

The liquid-chilled injector 140 cools the ozone and injects it closer tothe wafer 34, thereby decreasing the likelihood of prematuredissociation and oxidation of other chamber parts. It also tends to coolthe chamber wall 138 in its immediate vicinity.

A cross-sectional view of FIG. 6 taken along the chamber axis 18schematically illustrates the RTP chamber 10 in the vicinity of theprocessing space 50. The first and second gas inlet ports 120, 122extend in a plane perpendicular to the central axis 18. The second gasinlet port 122 may be located 90° about the axis 18 within that planefrom the first gas inlet port 120 supplying the ozone through thewater-chilled injector 140. The angular separation, preferably in therange of 15° and 115°, between the two processing gas inlets 120, 122delays the mixing of the ozone with the other gases. The injector 140for the ozone is located downstream from the inlet port 122 for theother gases as referenced to the rotation direction of the wafer 34. Thesecond gas inlet 120 is diametrically disposed from the pump port 126and placed above the unillustrated wafer port in the chamber wall 138.Diluent, nitriding, and hydrogen gases are supplied through the secondgas inlet port 122 so as to reduce any back pressure in the injector 140and in the gas supply line 136 supplying the ozone to it. The second gasinlet 122 does not require cooling so that it may be conventionallyformed of a gas supply line terminating in a recess 190 in the chamberwall 138, thus not interfering with the wafer port or its slit valve.

Gaseous hydrogen from a gas source 192 is metered by a mass flowcontroller 194 into the processing chamber 50 via the second gas inlet122 to increase the oxidation rate, if desired, in a process similar toin situ steam generation. The hydrogen gas may either be essentiallypure hydrogen or be part of a mixture, such as a forming gas havingabout 7% hydrogen and 93% nitrogen. It has been found that pure hydrogensupplied with the highly concentrated ozone to a fraction of 33%provides the desired high oxidation rate. It is believed that hydrogenincreases the concentration of oxygen radicals.

Gaseous oxygen may be supplied from the oxygen gas source 130 throughanother mass flow controller 198 to the second gas inlet 122 to act as adiluent to reduce the oxidation rate, which may be desired for very thingate oxides. While it is possible for the ozonator 134 to passadditional gaseous oxygen to the first gas inlet 120, the additionalflow would increase the back pressure in the injector 140 and its supplyline. An alternative diluent gas is nitrogen supplied from a gas source200 through a mass flow controller 202 to the second gas inlet 122. Thenitrogen is also used to purge the processing chamber 50. Other diluentgases may be used, for example, argon or helium.

Other processing gases may be used. For example, nitrous oxide (N₂O)supplied from a gas source 204 through a mass flow controller 206 actsas a nitriding gas. The nitrous oxide may be used when a film of siliconoxynitride is desired as the oxidation product. It may also be suppliedseparately from the ozone to effect a forming anneal. Gaseous ammonia(NH₃) may alternatively be used as the nitriding gas, or other nitridinggases may be substituted.

Although the gas distributions from both the first and second gas inlets120, 122 are non-uniform across the wafer 34, the wafer 34 is rotatingabout the axis 18 fast enough to time-average out the non-uniformity.

The RTP chamber illustrated in FIG. 1 is illustrative only. Other RTPchambers may be used with the invention. Other types of thermalprocessing equipment may be also use. For example, Jennings et al.describe in U.S. Patent Application Publication US 2003/0196996 athermal processing apparatus that scans a narrow beam of laser lightacross the surface of the wafer.

High-concentration ozone oxidation has been verified in an RTP chamber.The resultant oxide films have been observed to exhibit many fewerinterfacial defects, presumably arising from dangling bonds, than oxidegrown with oxygen radicals formed in a steam generator. Ozone oxidationhas been observed at wafer temperatures down to 600° C. and reasonableoxidation rates should occur at lower temperatures, for example, down to400° C. However, 800° C. appears more workable at the present time.Wafer temperatures of 1000° C. produce very low defects densities. It iscontemplated that future generations of integrated circuits will requireoxidation temperatures even lower than 400° C., perhaps even roomtemperature. Chamber pressures of between 3 and 5.5 Torr have been used,far below the safety limit of 20 Torr. Even lower pressures may be used.Ozone-based oxidation with 33% hydrogen has been observed to produce a 2nm oxide thickness for 1 minute of processing. Ozone flow rates need tobe maximized to achieve high oxidation rates.

The relatively low process temperatures achievable withhigh-concentration ozone allows the use of a chamber resembling an LPCVD(low pressure chemical vapor deposition) chamber 210, schematicallyillustrated in cross section in FIG. 7. A vacuum chamber 212 is pumpedto, for example, less than 10 Torr by the vacuum pump 124 through thepump port 126 formed in an annular pumping manifold 214 formed near itsbottom wall. A pedestal heater 216 is configured to a support the wafer34 across a processing space 218 in opposition to a showerhead 220 inthe upper wall of the chamber 212. A supply gas manifold 222 is formedon top of the chamber 210 to receive the highly concentrated ozonethrough one gas inlet port 224 and the steam generating gas H₂ through asecond gas inlet port 216. If required, a diluent gas, such as oxygen ornitrogen or other nitriding gas may also be controllably supplied,either through the second gas inlet port 226 or through separate ones.The gases mix and equilibrate in the gas supply manifold 222 beforepassing through a large number, typically at least 100, of smallapertures 228 formed through the showerhead 220 in an area overlying thewafer 34. The processing space 218 between the showerhead 220 and thewafer 34 may have a thickness of about 500 mils (1.2 cm) in comparisonto a wafer diameter of 200 or 300 mm. The pedestal heater 216 includes aresistive heater 230 powered by an electrical power supply 232 to heatthe pedestal heater 216 to a relatively low temperature, for example,400 to 700° C., needed for high-concentration ozone oxidation. Othertypes of electrical heating are known, such as RF susceptors. Thetemperatures of the showerhead 220 and the manifold 222 need to bemaintained at relatively low levels, for example, less than 400° C. andpreferably substantially lower, by for example water cooling to preventthe premature dissociation of the ozone.

The planar geometry made possible in the LPCVD chamber 210 by the narrowprocessing space 218, the wide showerhead 222, and the annular pumpingmanifold 214 provides good uniformity for ozone-based oxidation withoutthe need to rotate the pedestal 216. The high-concentration of ozoneallows relatively low oxidation temperatures provided by a simpleresistively heated pedestal. As a result, the ozone-based oxidation maybe performed in a relatively simple and inexpensive chamber and notimpose particularly high temperatures on the wafer 34.

Although oxidation of silicon is the most widespread use of theinvention, the invention is not so limited and different aspects of theinvention can be applied to oxidizing other materials.

The gas injector of the invention is not limited to injecting ozone orother oxidizing gases and may be used with other types of CVD.

The invention claimed is:
 1. A method of treating a silicon surface of asubstrate to be formed into an integrated circuit, comprising the stepsof: maintaining a silicon surface layer of said substrate at atemperature of less than 800° C.; and flowing into a processing chamber,maintained at a partial pressure of ozone of between 1 and 20 Torr andaccommodating said substrate, a processing gas comprising a nitridinggas and an oxygen-based gas mixture containing at least 30% ozone byvolume to react with and nitride and oxidize silicon existing within thesurface layer prior to initiation of the flowing step and to continue toform a layer of silicon oxynitride on the processing surface during aduration of the flowing step, wherein the ozone flows into theprocessing chamber through a first port and the nitriding gas flows intothe processing chamber through a second port.
 2. The method of claim 1,wherein said oxygen-based gas mixture contains at least 50% ozone byvolume.
 3. The method of claim 2, wherein said oxygen-based gas mixturecontains at least 70% ozone by volume.
 4. The method of claim 3, whereinsaid oxygen-based gas mixture contains at least 90% ozone by volume. 5.The method of claim 1, further comprising flowing hydrogen into theprocessing chamber.
 6. The method of claim 5, wherein the hydrogen flowsinto the processing chamber through the second port.
 7. The method ofclaim 1, wherein the temperature is less than 600° C.
 8. The method ofclaim 7, wherein the temperature is less than 400° C.
 9. The method ofclaim 1, wherein the gas mixture is not excited into a plasma adjacentthe substrate.
 10. The method of claim 1, wherein the maintaining stepincludes directing a plurality of incandescent bulbs at the substrate.11. A method of treating a silicon surface of a substrate to be formedinto an integrated circuit, comprising the steps of: maintaining asilicon surface layer of said substrate at a temperature of less than800° C., wherein the maintaining step includes electrically heating apedestal supporting the substrate; and flowing into a processingchamber, maintained at a partial pressure of ozone of between 1 and 20Torr and accommodating said substrate, a processing gas comprising anitriding gas and an oxygen-based gas mixture comprising at least 30%ozone by volume to react with and nitride and oxidize silicon existingwithin the surface layer prior to initiation of the flowing step and tocontinue to form a layer of silicon oxynitride on the processing surfaceduring a duration of the flowing step.
 12. The method of claim 11,wherein the flowing step includes flowing the gas mixture into a gasmanifold separated from the processing chamber by a showerhead includinga plurality of apertures therethrough and disposed in opposition to thepedestal.
 13. The method of claim 1, further comprising flowingmolecular oxygen gas through an ozonator external of the chamber toproduce the oxygen-based gas mixture.
 14. The method of claim 1, wherethe pressure is maintained no higher than 5.5 Torr.
 15. The method ofclaim 1, wherein the nitriding gas is chosen from the group consistingof ammonia and nitrous oxide.
 16. A method of oxidizing a surface of asubstrate to be formed into an integrated circuit, comprising the stepsof: maintaining a processing surface of the substrate at a temperatureof less than 700° C., wherein the maintaining step is performed byresistively heating a pedestal supporting the substrate; and flowing anoxygen-based gas mixture containing at least 30% ozone by volume from afirst gas port into a processing chamber accommodating the substrate andmaintained at a partial pressure of ozone of between 1 and 20 Torr,wherein the method reacts with and oxidizes a pre-existing layer at thesurface of the substrate to form an oxide layer from portions of thepre-existing layer and continues to form the oxide layer during aduration of the flowing step, wherein the pre-existing layer pre-existsprior to initiation of the flowing step.
 17. The method of claim 16,further comprising flowing hydrogen gas into the processing chamber. 18.The method of claim 11, wherein the temperature is less than 600° C. 19.The method of claim 1, wherein the processing gas does not include asilicon-containing gas.
 20. The method of claim 16, wherein nosilicon-containing gas is flowed into the processing chamber while thepre-existing layer is being oxidized.
 21. The method of claim 11,wherein the nitriding gas is selected from the group consisting ofammonia and nitrous oxide.